112 TRYPANOSOMES AND SLEEPING SICKNESS 



the bugs which he interprets as sexual reproduction. After about 

 ten days there occasionally occurs in the midgut of the bugs 

 round organisms with thick capsules, and in a few cases Chagas 

 has observed, after about six days, what seemed to be a division 

 of this body into eight individuals each presumably giving rise 

 to a trypanosome of a new generation. Whether or not the 

 infective trypanosomes arise in this way they appear in the mid- 

 gut from the eighth day onward. The occurrence of the infective 

 parasite in the salivary glands (Fig. 28G) is very irregular. The 

 fact that parasites have occasionally been found in the body 

 cavity of bugs suggests that the trypanosomes may make their 

 way through it to reach the salivary glands. As already re- 

 marked the trypanosomes in the bugs have never been found 

 infective before the eighth day, but once the infective forms have 

 developed they persist in the bugs for over a year. 



The barbeiro is not the only insect capable of acting as an 

 intermediate host for Trypanosoma cruzi. Several other South 

 and Central American species of Triatoma have been found to 

 be naturally infected with this trypanosome or with one mor- 

 phologically indistinguishable from it, and experimentally the 

 trypanosomes develop in the cosmopolitan species, T. rubro- 

 fasciata and other cone-noses and in bedbugs. Nor is man the 

 only vertebrate host. Experimentally apes, dogs and guinea- 

 pigs are subject to infection, and in nature the common Bra- 

 zilian armadillo, Dasypus novemcinctus, and various rodents have 

 been found infected, their infection undoubtedly being carried 

 by the common bug, Triatoma geniculata, which infests their 

 burrows. The fact that infected bugs occur in some places 

 where Chagas' disease is not known to occur suggests that, as is 

 the case with Trypanosoma rhodesiense and the trypanosomes 

 undistinguishable from it except by their harmlessness to man, 

 not all strains of the parasite cause human disease. It is inter- 

 esting to note that a very similar trypanosome has recently been 

 discovered by Kofoid and McCulloch in Triatoma protracta of 

 southwestern United States. This bug is common in nests of 

 wood-rats and frequently attacks man also. This discovery 

 suggests one of two things: either the trypanosome described 

 as T. triatomce, and which is admitted by the discoverers to differ 

 from T. cruzi only in slight characteristics of questionable im- 

 portance, is really identical with or a mere variety of T. cruzi, 



